U.S. & World

"I just don't think there's anything [left] to contribute – there's nowhere to take Sam," Shia told Access Hollywood guest correspondent Tim Vincent at the "Transformers: Dark of the Moon" premiere in Moscow on Thursday, when asked if he would be on board for a possible fourth installment. "I think creatively we've taken it as far as we can, and to do another one is purely a profit motive.

"I've given it my all and I'm proud of these three movies – I'm most proud of this third movie," he continued. "I feel like it's really hard to top this!"

In addition to his leading role in the robot action movies, Shia also starred in 2010's "Wall Street: Money Never Sleeps" alongside Michael Douglas — who was battling throat cancer at the time of the film's release – and Shia revealed he has maintained contact with his former co-star.

"He feels strong," he told Tim when asked how Michael's health is faring. "He's running again. He's back on the treadmill."

Catch Shia, along with Josh Duhamel and "Transformers" newcomers Patrick Dempsey and Rosie Huntington-Whiteley, in "Transformers: Dark of the Moon" – in theaters on June 29.